1. Field of the Invention
The invention relates to a cylinder device for a hydraulic brake system that is provided in a vehicle.
2. Description of Related Art
In US Patent Application Publication No. 2009/0179485, there is described a cylinder device. This cylinder device includes (a) a housing, (b) a first and second pressurizing pistons, (c) a first and second front pressurizing chambers, (d) a control chamber, (e) a control piston, (f) an input piston (a pressure member), (g) a pedal simulator piston, (h) a rod, (i) a simulator piston, and (j) a first and second springs. The pressurizing pistons are liquid-tightly and slidably fitted to the housing. The front pressurizing chambers are provided in front of the pressurizing pistons, and are connected to wheel cylinders respectively. The control chamber is provided behind the first pressurizing piston, and is connected to a hydraulic control device. The control piston is provided in a rear portion of the first pressurizing piston, receives a hydraulic pressure in the control chamber, and transmits a pressure to the pressurizing pistons. The input piston is coupled to a brake pedal. The pedal simulator piston is disposed behind the control chamber, and is restrained from retreating. The rod is extended backward from the control piston, penetrates the pedal simulator piston, and is slidably fitted to a recess that is provided in a front portion of the input piston. The simulator piston is disposed between the input piston and the pedal simulator piston. The first spring is provided between the simulator piston and the pedal simulator piston, and the second spring is provided between the simulator piston and the input piston. In this cylinder device, when the hydraulic pressure controlled by the hydraulic control device is supplied to the control chamber, the pressurizing pistons are advanced, and a hydraulic pressure is generated in each of the front pressurizing chambers and supplied to a corresponding one of the wheel cylinders. Besides, the input piston is advanced as the brake pedal is depressed, but the rod advances as the control piston advances. Therefore, a gap for the recess is ensured, and the input piston is permitted to move relatively to the first pressurizing piston. In the case where no control pressure is supplied to the control chamber, the input piston is advanced through depression of the brake pedal, and the pressurizing pistons are advanced via the rod. Besides, the pedal simulator piston is advanced to come into abutment on the control piston, and the first pressurizing piston is advanced.